Blind rivets which are comprised of a hollow metal rivet body with a sleeve, a flange formed on one end of the sleeve, and a metal mandrel with a shaft that passes through and projects out from a through hole in the rivet body, are well known. An advantage of blind rivets is that they can be used to join multiple workpieces, working from one side only.
The rivet body of a blind rivet has a flange formed on one end and a hollow, tubular sleeve which extends from the flange. The mandrel of the blind rivet has a long, narrow shaft which passes through the rivet body, and a mandrel head on the end of the shaft, which has an outer diameter larger than the inner diameter of the sleeve. The mandrel head is disposed contiguously on one end of the sleeve, on the side opposite the flange; the blind rivet is assembled by inserting the shaft of the mandrel in the through hole of the rivet body so that the shaft of the mandrel projects from the flange.
The assembled blind rivet is inserted into the hole of a workpiece such as a panel or the like, with the head of the mandrel going first, and the flange is made to abut the circumference of the hole of the workpiece. The flange is held by a fastening tool; when pulled strongly from the flange side while gripping the shaft of the mandrel, one end of the sleeve of the rivet body undergoes deformation by expanding in diameter, and the mandrel breaks at a narrow, breaking portion of the shaft. The workpiece can be fastened between the flange and the expanded diameter portion of the sleeve.
Blind rivets can be a peel type blind rivets in which cutting edges are formed on the surface of the mandrel head on the shaft side; during fastening, the cutting edges expand the diameter of one end of the sleeve of the rivet body by cutting it. Because a peel type blind rivet expands the diameter of one end of the sleeve by cutting it open, it is possible to fasten a workpiece by greatly expanding the diameter of one end of the sleeve.
However, because a peel type blind rivet uses the cutting edges of a mandrel head to cut open one end of the sleeve, this easily causes the defect of breakage if the mandrel is not pulled out in a steady and even fashion. Also, the length over which the cutting edges cut into the sleeve is variable, and if cutting is excessive, the broken portion of the mandrel shaft may project from the flange side of the rivet body. Also, when the sleeve is cut, great stresses are applied to the mandrel head and to the sleeve, and as a result, the mandrel head may fall off.
JP Patent Publication 2009-180347 discloses a peel type blind rivet having a rivet body comprised of a cylindrical barrel and a flange-shaped head formed on one end of the barrel; a shaft that is inserted in and passes through the rivet body; a large diameter head formed on one end of the shaft; and a neck portion formed on the mandrel, which is used for breaking. The inner diameter portion of the blind rivet of 2009-180347 has a large diameter portion on the barrel side and a small diameter portion on the side of the head. The mandrel has a rough, indented and raised portion on the surface of the shaft between the head and the neck, which is formed along the lengthwise direction of the shaft. When the fastening is completed, the raised portion of the mandrel wedges into the inner surface of the small diameter portion of the rivet body, securing it strongly, thus preventing the mandrel from falling off. The indented and raised portion has the shape of a saw blade, and the surface of the raised portion on the neck side is slanted, so that the load needed when the mandrel is inserted into the rivet body is small.
However, machining the raised and indented portion in the mandrel of the blind rivet of 2009-180347 requires effort and is costly.
Also, in order to have the raised portion of the mandrel wedge into the inner surface of the small diameter portion of the rivet body, it is necessary to pull in the mandrel until the raised portion which is contiguous to the mandrel head goes over the large diameter portion of the rivet body and reaches the small diameter portion. For that reason, a large load is needed to pull the mandrel in, and it is not possible to prevent the rivet body from breaking. Furthermore, the head of the mandrel may fall off when a thick workpiece is fastened.
JP Patent Publication 59-131012 discloses a blind fastener (blind rivet) which is provided with a hollow sleeve having a sleeve shaft and a large sleeve head, and a pin (the mandrel) having a shaft and a thick head portion. Although the blind rivet of 59-131012 widens the shaft portion of a sleeve by means of the head portion of a pin, it is not a peel type blind rivet.
The blind rivet of 59-131012 uses the portion of the through hole of the sleeve that has a narrow diameter as a stop shoulder, and a securing groove is formed in the pin. During fastening, the head portion of the pin widens the end of the sleeve shaft and moves through the center of the sleeve shaft. When the stop shoulder enters the securing groove, the movement of the pin stops; when the relative force applied to the pin and the sleeve reach a pre-determined level, the pin breaks at a breaking groove on the neck.
The blind fastener of 59-131012 strongly secures the pin and sleeve since they are secured mechanically by means of the movement of the stop shoulder of the sleeve into the securing groove of the pin.
However, in the blind fastener of 59-131012, when the stop shoulder of the sleeve and the securing groove of the pin are in the same position in the axial direction, the material of the stop shoulder of the sleeve flows into the securing groove of the pin and is secured. As a result, this determines the relative position in which the sleeve and pin can be secured. For this reason, the range of thicknesses for the components to be attached is narrow, and as a result, a problem arises in that the workpiece cannot be fastened if it is thicker or thinner than this range of thickness(es).
For this reason, a peel type blind rivet is sought in which, during fastening, breakage of the rivet body is controlled, the broken portion of the mandrel does not project from the surface on the flange side, and the mandrel head does not fall off such that fastening can be done in a controlled manner. In addition, a peel type blind rivet is sought which can fasten workpieces with a broad range of thicknesses.